1. Field of the Invention
The present invention relates to a motor vehicle body structure employing a sandwiched structural body which comprises a core layer whose opposite surfaces are covered with outer skin layers.
2. Description of the Relevant Art
Composite structural bodies mainly made of synthetic resin or reinforced plastic, instead of steel sheets, have recently been proposed and used in motor vehicle bodies for the purposes of reducing the weight of motor vehicles and also increasing productivity of motor vehicles.
Such composite structural bodies are generally in the form of a sandwiched structural body comprising a core layer whose opposite surfaces are covered with outer skin layers. The core layer may be made of foamed plastic (see, for example, Japanese Patent Publications Nos. 46-36329 and 55-43912, Japanese Laid-Open Utility Model Publication No. 63-30276, U.S. Pat. Nos. 4,559,274 and 4,573,707), or of a honeycomb structure (see, for example, Japanese Laid-Open Patent Publication No. 47-32521, Japanese Laid-Open Utility Model Publications Nos. 57-114774, 62-174935, and 62-174978). It has also been proposed to use, as a motor vehicle body, a sandwiched structural body with a hollow space in a core layer, as disclosed in Japanese Laid-Open Utility Model Publication No. 62-166136, for example.
Modern motor vehicles such as automobiles mostly have a monocoque body that combines a frame and a body together and which serves as a frame for bearing applied external forces as they are distributed over the entire monocoque body. The monocoque body is advantageous in that the entire motor vehicle weight is reduced, and the motor vehicles can be produced at an increased production rate and with less cost.
Therefore, it is preferable that motor vehicle bodies in the form of composite structural bodies of synthetic resin, reinforced plastic or the like be also of a monocoque structure for reduced motor vehicle weight and increased productivity. Demands for composite structural bodies as monocoque motor vehicle bodies are growing.
However, if a monocoque motor vehicle body were assembled from a plurality of components in the form of sandwiched composite structural bodies mainly of synthetic resin, as with conventional steel sheets or the like, then the assembled monocoque body would not be sufficiently mechanically strong, durable, and shock-resistant.
There has been proposed a joint structure for joining a floor panel and a pair of side frames in a basic frame assembly for a motor vehicle body structure, the floor panel and the side frames being in the form of sandwiched structural bodies, as disclosed in Japanese Utility Model Application No. 1-72061.
Although each of the components of the proposed frame assembly is sufficiently mechanically strong, durable, and shock-resistant, it is desired that the assembled motor vehicle body structure should be of higher rigidity against torsional and bending stresses.
Furthermore, the assembled motor vehicle body structure should also be strong enough to support various mechanical components including front suspension beams, upper arms, and an engine with sufficient mechanical strength, and to have increased shock resistance in various body regions.
In view of the foregoing demands, there have been proposed component attachment structures of a motor vehicle body in the form of sandwiched structural bodies, i.e., component attachment structures for front suspension beams, front suspension upper arms, and an engine (see U.S. patent application Ser. No. 446,429 filed Dec. 5, 1989 now U.S. Pat. No. 5,060,975, and European Patent Application No. 89312811.6 filed Dec. 8, 1989).